1108.5177 (Aninda Sinha et al.)

Implications of a viscosity bound on black hole accretion    [PDF]

Aninda Sinha, Banibrata Mukhopadhyay

Motivated by the viscosity bound in gauge/gravity duality, we consider the
ratio of shear viscosity (eta) to entropy density (s) in black hole accretion
flows. We use both an ideal gas equation of state and the QCD equation of state
obtained from lattice for the fluid accreting onto a Kerr black hole. The QCD
equation of state is considered since the temperature of accreting matter is
expected to approach 10^{12}K in certain hot flows. We find that in both the
cases eta/s is small only for primordial black holes and several orders of
magnitude larger than any known fluid for stellar and supermassive black holes.
We show that a lower bound on the mass of primordial black holes leads to a
lower bound on eta/s and vice versa. Finally we speculate that the
Shakura-Sunyaev viscosity parameter should decrease with increasing density
and/or temperatures.

View original: http://arxiv.org/abs/1108.5177